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Animal Protein and the Cancer Promoter IGF-1

For years we didn’t know why eating a plant-based diet appeared to so dramatically improve cancer defenses within just a matter of weeks. But researchers recently figured it out: eating healthy lowers the level of the cancer promoting growth hormone IGF-1. This saga was detailed in my last four blog posts:

What is the mechanism by which a simple dietary change can alter the levels of this cancer promoter? Imagine you’re a kid with some tinker toys. Then for your next birthday you get one of those huge tinker toy sets dumped down in front of you. All excited with this new load of raw building materials, you may really start scaling up. Basically it’s the same with your liver and insulin-like growth factor 1.

When we dump a load of protein in our body, our liver’s like, “Whoa, look at all this! What are we going to do with it all? We can’t just waste it, we’ve got to do something with it!” So our liver starts pumping out IGF-1 to tell all the cells in our body “It’s growin’ time! Be fruitful and multiply. Spare no expense, go crazy—look how much excess protein we got to work with!

The problem is that some of the new additions spurred by this growth hormone may be tumors. When you’re a fully-grown adult, cell growth is something we want to slow down, not accelerate. The goal, therefore, would be to maintain adequate, but not excessive, overall protein intake.

Wait a second, though. As I show in my 3-min. video Protein Intake and IGF-1 Production, studies have found no association between total protein intake and IGF-1 levels. But that’s because they didn’t take into account animal versus plant protein. It took a study comparing meat-eaters to vegans to show that higher IGF-1 levels were only associated with animal protein intake. In fact, plant protein seemed to decrease IGF-1 levels. Animal protein appears to send a much different signal to our livers than most plant proteins. Even vegans eating the same amount of protein as meateaters still had lower levels of the IGF-1, so it’s apparently not about excessive protein in general, but about animal protein in particular. To understand why, see my 3-min. video Higher Quality May Mean Higher Risk.

If the reason animal proteins raise IGF-1 levels is because they resemble our own proteins, what about the few plant proteins that just coincidently happen to have amino acid ratios similar to proteins such as soy? Great question! That will be the subject of my blog post on Tuesday.

For those who haven’t been following along, see IGF-1 as One-Stop Cancer Shop for the reason we’re so concerned about IGF-1 levels and my videos The Answer to the Pritikin Puzzle and How Plant-Based to Lower IGF-1? to learn about the role diet plays in cancer development.

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

80 responses to “Animal Protein and the Cancer Promoter IGF-1

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        1. Hi, tatu bearcroft. While it is well-known that many practices are used in large-scale animal agriculture operations to reduce the amount of time it takes for an animal to be large enough to slaughter, that is not really what the study you included is about. It is about the effect of nutrition on reproduction in female sheep. I think this might be more along the lines of what you are asking:
          I hope that helps!

  1. I see your credentials say “MD” so I’ll assume you’re not an oncologist? Perhaps talking out of your depth a touch.

    Perhaps you can lend some clarity to your readers and specify that IGF-1 presence can contribute to increased growth of EXISTING cancer cells? Or that IGF-1 is needed for people who are hoping to grow, like say, children?

    . . . but I guess it’s fun for a GP to write scare stories.

    1. If you are interested in Dr. Greger’s credentials, you can read all about them here and here.

      And, if you actually watched the IGF-1 videos you’d see that Dr. Greger provides plenty of context about IGF-1.

      Specifically, you might want to start here:
      IGF-1 as One-Stop Cancer Shop
      . The synopsis clearly states “Insulin-like growth factor (IGF-1) is a natural human growth hormone instrumental in normal growth during childhood, but in adulthood can promote abnormal growth—the proliferation, spread (metastasis), and invasion of cancer.” Moreover, the video provides plenty of context and clarity.

        1. Saint Jude already holds that designation.

          You keep sparing the lives of organisms you deem worthy. I’ll keep eating/wearing them.

          By the way, as a vegan (yes I’m absolutely intent on antagonizing the lot of you) where do you draw the line? You don’t eat meat.
          Do you swat a mosquito? (Still an animal)
          Do you use antibacterial soap? (Prokaryotes are animals)

          Go on and tell me how insects and bacteria somehow don’t count, by your arbitrary definition of intelligence. OOH! Tell me about how I’m not as intelligent as a bacteria, I’ve never heard that one before.

          1. Caveat emptor are you in England? We had such fun there a few year back. (“The lot of you”)

            I am a vegan for health reasons. I have severe heart disease on my father side so best for me to go with best current data. Very young death of my father, his brother and my grandmother.

          2. Many here are vegans for health, and are not as radical as you seem to think. The science is in favor of consuming a plant based diet, trying to insult people who don’t eat meat is a great approach to lose credibility.

          3. If you look up the definition of veganism, you will see things like “cause as little harm as possible”, “avoid violence”, or “live without exploiting”.

            So there are no claims or expectations of perfection. I found out a while that nalgene is big into the animal restraining devices and cages for animal testing. Who knew? And I just found out yesterday that the media I use to grow bacteria has casein in it. So from now on I’ll avoid nalgene and do some research into alternative media. For ethical vegans, it’s a simple desire to reduce the amount of harm one inflicts on others. It is indeed a complex topic as you mentioned, and it is a learning process.

            Have you ever heard phrases like “just because you can’t do everything, doesn’t mean you shouldn’t do anything”, or “don’t let perfect be the enemy of good”? These are ideas that I think many ethical vegans go by.

            And as others have said, since this is a nutrition website, if you truly wish to antagonize the animal rights crowd you will probably get a better response elsewhere.

      1. Grand.

        You’ve got to delve pretty deep into his postings to get to the part where, reading between the lines, you uncover the fact that IGF-1 poses no measurable detriment to the non-cancer-ridden among the global population.

        Calling IGF-1 a One-Stop Cancer Shop, or Cancer Promoter is irrefutably fear-mongering.

        Particularly since the bulk of readers come from a facebook link. We all know facebook readers are ultra-dilligent.

        And still I stand behind the fact that this charming Woolie-Willy impersonator is a GP, not an oncologist.

        1. I don’t think you have to delve that deep at all. One just has to actually click on the links mentioned in the blog post and watch them. It’s not “in between the lines” it is actually in the lines.

          Maybe I have more faith in the intellect of the people visiting this site than you do (regardless of how they are introduced to this site). I like to think that those accessing this site use critical thinking (and reading) skills while reviewing the information provided.

        2. I’m not an oncologist either, but I can still use Medscape, Medpub and F1000 to look up peer reviewed medical studies. If you have a point to make regarding credentials, you’ve failed to do so.

          I have no problem with the killing of animals for food, and again fail to see your point in asking if we have a problem swatting a fly. So far, you’ve failed to communicate your point.

          Perhaps if, in your next post, you’ll skip the rhetoric and assumptions and actually make an evidence-based statement, there will be something substantive to address.

          1. And I fail to see your point, other than stubbornly refusing to give up the notion that you can do anything you want without consequences, credentials aside.

        3. I forget which video it’s in, but Dr. Greger discusses a study in which researchers did autopsies on Japanese men who had died of other causes, to determine the rate of prostate cancer. It was determined that Japanese men and American men get prostate cancer at the same rate, yet American men have 10x the death rate from it. The cancers in the Japanese men were still small and had not yet proliferated enough to cause problems.

          Also there was another study done on the rates of cancer in young people who had died of other causes. Again, they had plenty of cancer, albeit little bitty ones.

          So I think what you’re missing conceptually here, is that we all have cancer. We are all constantly getting cancer, all throughout our lives. Even in a world completely unadulterated by industrial toxins and the like, we would still have carcinogens like uv light, radon, etc, and even routine cell division can lead to mistakes and bumps in the DNA that don’t get repaired. It’s a constant battle between damage and repair. Most people think they “get cancer” when they’re diagnosed with it at say 50 or 60 years old, but this is after the cancer has a few decades of cell division under its belt, and is now at the point that it’s actually become noticeable.

          So since we’re all getting cancer, all the time, one may assume that the trick is simply keeping it in check. In societies where people are basically taking preventative chemotherapy in the form of vegetables and green tea every day of their lives, we see less cancer. In societies like ours, with little of the cancer fighters in our diet, but replete with cancer promoters, we see more cancer.

          I hope this puts some new light on the topic for you, as it seems clear that there is no such thing as the “non-cancer-ridden” among us, and that for all practical purposes, promotion and causation may be looked at as one and the same. In fact, since there is no way to truly “prevent” cancer, our only choice is whether to treat it or promote it.

          Also, your criticism of Dr. Greger’s credentials is unfounded. An oncologist knows the trade of treating cancer, with the standard treatments available today. The more adventurous may conduct clinical trials with experimental treatments. However they would not necessarily be any more qualified than Dr. Greger to discuss this sort of topic, as they are not epidemiologists nor molecular biologists. Dr. Greger on the other hand, pretty much devotes his life to studying the latest cancer research from all relevant fields.

          Does anyone remember which video I’m talking about?

    2. The oncology departments have been extremely successful at completely
      ignoring the anti-cancer phytonutrients science while fitting into the perfect
      “drug pusher” role. What a shame that you aren’t providing your credentials and real name “Caveat emptor”. I assume that your credential can be hidden under “Caveat emptor”.

  2. Thanks a lot for your explanations. Even if your posts recap information that’s already in the videos, I find them very instructive. Toni from Reus (Spain).

  3. Caveat emptor works for the food corporations..He’s the butcher in the back picking the meat up off the floor and wrapping it up for the customers.. that’s his creds.

  4. There is indeed some evidence that IGF-1 encourages growth of cancers, but that does not mean it causes cancer, and it certainly does not mean that eating (non factory) meat and dairy foods cause cancer either.

    Cancer is a modern disease. But there are plenty of culture that have eaten lots of meat for a long time (inuit, prairie indians, Australian aborigines etc) that never got cancer until they started eating modern foods.

    similarly, there are numerous cultures that have eaten dairy foods for a long time (Swiss, Scandinavians, Greeks, Masai, Tuoli (of NW China)) and they didn’t get cancer either, until they started eating modern (i.e. processed grain based) foods…

    We can’t say the same about a historical veg*n culture as there has never been one (which says something in itself).

    Cancer cells usually have more insulin receptors than normal cells, and there is evidence that targeting IGF alone doesn’t get great results, you need to target insulin itself (i.e. minimize it)

    This is why certain types of ketogenic diets have been effective on some cancers when all else has failed.

    So, people have been eating meat forever, and dairy for millenia, yet cancer was exceptionally rare until just over a century ago.

    So what changed? Certainly not the amounts of meat an milk being eaten…

    1. Paul N You raise some interesting points. The increase in processed foods and factory farming has an impact in the current health epidemics, to be sure. While it may be true that humans have eaten dairy and meat in the historical past, I think that it would be fair to say that the amount that is consumed by people these days is, in fact, much more than in the historical past and that it probably has a role to play in our modern day health epidemics as well.

      All in all, it seems to me based on both historical and current scientific evidence, that humans, have been and probably should be plant-based eaters, whether that be vegan or not is probably not as important.

      As for a “historical vegan culture”, your point is a good one, but I think there are plenty of vegans in the world to account for a “historical culture”, even if it is not geographically concentrated. And, given the number of such plant-based eaters, there are plenty of them that studying their eating habits and health makes empirical sense regardless of whether they existed as a “historical culture” or not.

      1. Chomper,

        ” I think that it would be fair to say that the amount that is consumed by people these days is, in fact, much more than in the historical past and that it probably has a role to play in our modern day health epidemics as well.”

        I that really fair to say? Lets take a look..

        According to USDA data, the per capita milk production from 1961 to 2011 decreased from 318L to 287 – so no increase there. Actual milk and butter use was higher still in the 1910’s..

        Beef peaked in the early ’70’s and is no back to the same per capita as in 1909. Pork has been about the same all century.

        There has bee a seven-fold (!) increase in poultry consumption (almost all grain fed) since the 40’s.

        So a century of rising cancer (and other disease) rates, but no real increases in dairy, beef or pork consumption – so I’d say they are off the hook .

        Wonderful stuff, data…

        But I do agree with your basic premise that if there are things we are eating a lot more of now, than a 100 years ago, then they are at least a suspect.

        So poultry is clearly indicted, what else might have changed?

        Wheat has dropped from 225lbs/capita in 1879 to 188 in 1925 and 110 in 1972, and has rebounded to 132 in 2012.

        At first appearance, it gets off, thought the change to dwarf/GMO wheat in the 80’s, and the increasing rates of celiac mean we’ll keep that file open.

        Saturated fat consumption?

        Lard went from 12lbs/cpta/yr in 1910-50 to an astonishing 0,5lbs in the early 90’s – no smoking gun there.

        Butter went from 18lbs/c/yr in 1909 to 4 in 2001, so no dice there either..

        beef tallow, well, I can’t find any figures, but after Mcdonalds famously stopped using it for fries in 1990, switching to “healthy” vegetable oils, I’d say its consumption is near zero.

        Speaking of vegetable oils, what about soy oil, and the “heart healthy” omega-6 oils in general?

        Well, from 1909 to present, n-6 consumption has tripled, and soy oil has gone up by a factor of 1000(!), most of that since the ’50’s.

        I think we may have a winner!

        Of course, lots of the resulting soybean meal got fed to the chickens…

        So, be honest here, if you had to bet your house, or your first born, on what has really caused the increases in non-communicable diseases (incl cancer) in the 20th century, would you bet your childs health and future on dairy and red meat, or would you bet on (soy fed) chicken, and soy oils?

        These data don’t lie – we eat less dairy and red meat than ever, and are getting sicker – they can’t be the root cause.

        1. Milk and butter consumption may be down, but overall dairy consumption is still way up. Cheese and yogurt consumption have risen many times over from what they used to be. It takes 9 gallons of raw milk to make just one pound of cheese, so is wrong to say people are having less dairy. In reality they are having more and that dairy is much more concentrated in fat, calories, etc. Data is a wonderful thing, but you can’t just pick and chose the information you want to use while excluding the rest that doesn’t support your argument. You made that same point yourself when comparing beef/pork to overall meat consumption. Animal proteins are all about the same as far as the body is concerned so how much of one vs. another really doesn’t make much difference. Saying that beef or pork went down cannot prove anything if other animal proteins went up in their place.

          Historically you are right that many people and cultures have eaten meat, but there is no way to say that they didn’t have cancer. Diagnosing cancer was impossible back them because people didn’t know what it was and technology wasn’t there to identify it. We have no way to know how it affected their health. What we do know was that the average lifespan was much much shorter than it is now. Historical arguments that are based on assumptions have no real place in modern day discussions, and many modern day cultures show that lower animal foods and higher plant foods do in fact create lower levels of disease. Look at the “Blue Zones” study done my National Geographic. That wasn’t even a study if nutrition, but they found that to be true.

          It’s also untrue to say that there haven’t been any vegan cultures. They may not have had that label, but many places in India, Asia, South America and others have followed a diet that was largely or completely vegetarian for centuries. It’s ridiculous to imply that a culture had to abstain from all animal products 100% to have eaten a vegetarian based diet. A small little piece of meat cooked into a dish once a week is hardly comparable to what people eat now. Based on all the studies I’ve read, there is good evidence to support that many people around the world have eaten largely vegetarian diets. Sometimes for no other reason than that meat and dairy were luxuries that they couldn’t afford.

          There are plenty of arguments that can be made on this issue, but studies are often flawed and people tend to pick out just what they want to use to prove a point just as you did, so lets keep it simple. I have personally read hundreds of case studies on people who have reversed devastating and life threatening diseases by following a whole foods diet that excludes meat, dairy, and eggs. Statistically vegetarians weigh less, live longer, and have lower rates of disease. Statistically “vegans” , meaning simple people who avoid dairy and eggs in addition to meat, have lower rates of disease than vegetarians. You are right that there are plenty of vegan nuts and I’m sure there are unhealthy vegans as well since eating vegan does not mean eating healthfully, but even with that, the statistics are still in their favor. That added to my own personal experience tells me that I feel better and have better indicators of health (lower BP, smaller waistline, etc) when I eat whole foods and avoid animal products. If that isn’t a reality for you, then you have every right to make a different choice. Just please stop belittling mine. If you have never tried a vegan diet than you really have no right to speak on it anyway since anything you have to say is uninformed. I respect your right to make your own choices, but I do no respect people who come to our tables with hateful and biased opinions. Argue the science with science, not the half truth opinion laden posts you have written here. If you don’t have any real facts to bring to the table, I would suggest you take the time you spend writing uninformed and rude comments to do some more reading more and keeping your mouth shut.

          1. Nikki,

            Hmm, I’m not even sure where to start, or stop, in reply to that outburst…

            but since this site is called “Nutrition *facts*” I think I’ll stick to those…

            “but overall dairy consumption is still way up.”

            So where are your facts to show that? If the per capita milk production is decreasing, how can overall (per capita) consumption be increasing?

            “It takes 9 gallons of raw milk to make just one pound of cheese,”

            No, it doesn’t. I get about a pound from one gallon of milk. But you likely won’t take my word for it, so, from Henning’s Cheese in Wisconsin; “It takes about 10 pounds (5 quarts) of milk to make 1 pound of whole milk cheese.”

            That’s 1 1/4 gal – you are out by a factor of 7.

            “Saying that beef or pork went down cannot prove anything if other animal proteins went up in their place.”

            Sure it can. Disease rates only started rising, as they seem to have, when chicken went up and beef went down, then is beef really the cause? And there are other differences between meats than just proteins – chicken (especially soy-fed) has very high levels of (easily oxidised) omega-6. And ruminants meats have vaccenic acid, CLA and a few other goodies too.

            The blue zone example is really good, the sardinians eat meat and cheese, the okinawans fish and pork, the SDA’s eat cheese and eggs.

            But they ALL eat a whole foods diet and minimise/elmininate factory processed foods.

            So, I return to this [still unanswered] question of just what defines a “plant based” diet?

            “I have personally read hundreds of case studies on people who have reversed devastating and life threatening diseases by following a whole foods diet that excludes meat, dairy, and eggs.”

            That’s great to hear. And I have read hundreds of cases of people who did the same while eating a whole foods diet with lots of meat, dairy and eggs. I also know several, including my partner and sister, that suffered serious health problems on a [soy containing] vegan diet that were only reveresed when they went back to including animal foods.

            Can you see the common factor – “whole foods”! As soon as we eliminate the modern factory farmed and processed foods, our health improves. There are certainly some that do better with less/no animal foods, and others that do better with much more. That is hardly damning evidence against animal foods?

            ” I do no respect people who come to our tables with hateful and biased opinions.”

            I don’t harbour any hate, nor do I think I have said anything even close {and the moderator can delete if they feel otherwise} We all have our own – often dissenting – opinions, and there is nothing wrong with that.

            If by “our tables” do you mean veg*n? I saw zero mention of that in the “about” page, is this a condition of posting here?

            This site is called “nutrition facts”, and I have discussed those presented and brought forward some others – that seems totally in keeping with the mission of this site.

      2. @ Chomper part 2…

        ” it seems to me based on both historical and current scientific evidence, that humans, have been and probably should be plant-based eaters, whether that be vegan or not is probably not as important”

        Well, depends on what you mean by this vague term “plant based”? Does that mean “plant only”, or “majority plants”, or “no meat”, or what?

        No one argues that man has been eating plants since forever, but whether we should be eating only plants is a whole different question.

        “I think there are plenty of vegans in the world to account for a “historical culture”, even if it is not geographically concentrated. And, given the number of such plant-based eaters, there are plenty of them that studying their eating habits and health makes empirical sense regardless of whether they existed as a “historical culture” or not.”

        Well, the two are not the same thing. Lets start with the fact there has never been a single veg*n culture – that means for many generations.

        Lots of veg*ns for one, or even two generations is not the same.

        Maybe you are familiar with Pottenger’s cats – the ones that didn’t get fed eat raw meat, got progressively less healthy over several generations, suffered degenerative diseases and died out by the third and fourth generation. Turns out they were missing a single nutrient – the amino acid taurine – which is deactivated by heat – and that they can’t make themselves.

        What might be an example of a critical nutrient missing from a human veg*n diet – b12? True vit A (retinol), K2 (MK4 form) Might there be more that we haven’t yet identified?

        Look at the studies of women having pregnancy problems on vegan diets.

        Couple this with the historical absence of a veg*n culture – out of the *thousands* that have existed – not even *one* went (and survived) vegan. How can you say that we “should be” when there *never* has been? The entire length of human history – the cumulation of trillions of lifestyle decisions – has zero examples to support your “should”.

        I will concede that, with enough artificial supplements of missing/deficient nutrients, and eating a variety of plants from all over the world, it is possible in modern times to survive, and be healthy, on a vegan (all plant based) diet.

        But absent modern technology and long distance food trade (i.e. eating locally and seasonally) it just can’t be – and never has been – done.

        Humans have been eating meat (and dairy) for infinitely longer than we have been eating “plant based” – it’s up to the multi generational vegans to prove that it can work.

        And I’m not using my loved ones as test cases.
        Like the cats, your mileage may vary.


      3. I think you are all missing something. It is not purely a question of what you eat. It is also a question of your genetic makeup. My family for generations have been meat eaters and no one in my family has ever suffered from cancer. Past or present.

        I don’t think a person should take this site as gospel and should seek a professional’s advise.

  5. TC Cambell in “The China Study” warned us about casein in excess, but it seems any complete protein in excess (including soy) stimulates GH, IGF-I, cancer proliferation, and shortens lifespan. has about 1300 papers relating to methionine restriction as an adjunct to cancer therapy (,19), so there’s very definitely interest in the medical community in “incomplete” proteins reducing IGF-I and cancer proliferation. And its not just methionine, perhaps any essential amino acid in deficit can reduce IGF-I ( Methionine is just very convenient as its easy to design low methionine vegan diets for cancer prevention and longevity (

    It seems likely that an ideal diet for longevity and chronic disease prevention is not the ideal diet for body building (whether omni or vegan). To my knowledge, there’s only anecdotal evidence regarding higher cancer incidence and shortened average lifespan in body builders, though it would be most interesting.

    Moreover, sarcopenia (aging related muscle loss) will affect all of us who survive long enough, so a diet (whether vegan or omni) minimizing GH/IGF-I might not be ideal for quality of late-life. Getting the information out about these tradeoffs makes it possible for people to decide how bright and long their candle should burn.

    1. In the study:

      Crowe, Francesca L., et al. “The association between diet and serum concentrations of IGF-I, IGFBP-1, IGFBP-2, and IGFBP-3 in the European Prospective Investigation into Cancer and Nutrition.” Cancer Epidemiology Biomarkers & Prevention 18.5 (2009): 1333-1340.

      eggs were found to increase IGF-I by an average 0.14% for every increase of 0.4% of calorie intake they represented. As a single large hard boiled egg is 4% of a daily 2000 kcal diet, it would be expected to increase serum IGF-I by 1.4%.

      This increase was less than observed from other animal products (see table 2), perhaps owing to egg albumin being an incomplete protein.

      Perhaps more importantly, for every increase of 0.4% of calorie intake from eggs, the serum levels antagonistic IGF binding proteins 1 & 2 declined by 0.93% and 2.46%, so a single hard boiled egg in a 2000 kcal diet on average decreased IGFBP-1 by 9.3% and IGFBP-2 by 24.6%

        1. As a vegan, the really interesting thing about Table 2 in that study was the different effects of starch and sugar. One assumes that the common high-glycemic index starches would be broken down almost instantly by amalase so the effects would be similar, but NO.

          The 140 calories of sugar in a 12 oz Coke appeared to increase serum levels of IGF-I by 0.7% while decreasing IGFBP-1 and IGFBP-2 by 5.5 and 3.3% respectively. Get the same 140 calories from a couple slices of white sugar-free bread and IGF-I declines by 1.1% and the binding proteins increase by 2.1 and 4.2% respectively.

          Granted, all of these attributed correlations may say more about overall dietary patterns (people were eating beans OR cola) in the cohort than the macronutrients themselves, but I found the distinction, particularly on the binding proteins, pretty remarkable. The glycemic indices don’t seem enough to account for it, so maybe there’s some involvement between fructose (half of dietary sugar but not present in starch) metabolism in the liver and IGFBP production.

        1. Nearly all proteins will have some leucine and methionine, just as nearly all long paragraphs include the letters ‘e’ and ‘g’ (1st and 17th most common letters). Free leucine is the most potent amino acid signal for growth signalling, and like IGF-1, its pathway converges on mTORC1, a master regulatory hub for nutrient signalling, protein synthesis, and growth:

          When mTORC1 in hypothalamic cells is activated, it both supresses hunger (the major reason people lose weight on Atkins) and causes release of growth hormone. Liver cells respond to circulating growth hormone by releasing IGF-1 and other insulin-like growth factors. Nature likes these Rube Goldberg contraptions, perhaps because they offer more potential points of regulation – IGF activity is controlled still further downstream by circulating IGF-binding proteins.

          While its known that methionine levels impact IGF levels, the point of control isn’t as well understood as with leucine. Methionine restricted diets may be having more important effects in limiting cancer growth by limiting methyl donors for DNA methylation, by limiting protein synthesis directly (its the first “letter” in every protein), or by simply reducing mitochondrial oxidative stress.

        2. Just adding to my last comment: there is another plausible pathway for dietary restriction/moderation in any amino acid to reduce IGF-1:

          • Deficiencies of any amino acid cause accumulation of uncharged transfer RNA (rare in the protein replete state).
          • Uncharged transfer RNA binds to GC nonderepressing 2 kinase (GCN2), inducing phosphorylation of eukaryotic initiation factor 2 (eIF2a) 1
          • Phosphorylated eIF2 increases transcription of activating transcription factor 4 (ATF4) 2
          • ATF4 binds to the two sites in the promotor of the FGF21 gene, increasing its transcription 3
          • FGF21, by blocking activation of STAT5, reduces liver IGF-1 production 4

          I learned about this pathway from Mark McCarty’s newest paper.

          The advantage of methionine (or lysine) restricted or moderated diets in reducing IGF-1 is that they’re quite practical with certain plant based diets.

      1. And how did proteins from animal muscle fare in that Crowe analysis compared to proteins from milk or eggs? To what degree is effect on IGF binding proteins important? Are certain binding proteins more effective at decreasing total IFG-1 than others? And what do you make of the studies showing a U-shaped curve with respect to IGF 1’s influence on cancer, cancer mortality, total mortality? Thanks, as always, for your insights, Darryl.

        1. Increments in protein intake from meat had an effect on IGF-1 levels comparable to eggs and less than that from milk. Each 2.5% increment in daily calories from meat protein increased IGF-1 by an average of 0.89%, and 2.5% is 13 g protein in a 2000 diet, the amount in 1 ½ oz boneless / skinless chicken breast (a rather tiny serving).

          If I divide the IGF1 increment for SD increments in protein intake by the size of that SD increment in table 2, I can obtain a not so reliable estimate of the IGF-1 increase for every 1% of calories from these protein sources:

          Meat: 0.35%
          Eggs: 0.35%
          Seafood: 0.36%
          Dairy: 1.31%

          As you can see, dairy protein is a uniquely effective IGF-1 inducer. This paper offers a new explanation for why:

          Melnik, B. C., John, S. M., & Schmitz, G. (2013). Milk is not just food but most likely a genetic transfection system activating mTORC1 signaling for postnatal growth. Nutr J, 12, 103.

          Got microRNA-21?

          The IGF binding proteins are very important, as they’re present in higher concentrations than IGF-1 in plasma, and are used by the body to moderate the effects of IGF-1. Most circulating IGF-1 is actually in a bound state. Biolological / evolved systems like these Rube Goldberg-esque signalling mechanisms, as they provide more points of control, without requiring the physical wiring and “computation” of an engineered system. Similar regulation occurs with sex hormones.

          I’m no expert on IGFBPs, but my understanding is IGFBP-3 is considered the main binding protein due to having by far the highest plasma concentrations. If I had more time I’d look into what is known about the IGFBP’s binding affinities, which would tell us how likely each IGFBP will hold onto a IGF-1.

          With respect to U-shaped associations, its important to consider reverse causation. IGF-1 levels naturally decline with age, and the elderly are much more likely to have diagnosed cancer and other morbidities. Its a similar situation to cholesterol, which also declines in the very elderly and those near death. So I don’t think whole diagnosed population studies offer a clear picture – instead I’d be more interested in age-adjusted correlations between IGF-1 and mortality restricted to younger cohorts.

          1. Darryl: That was a really interesting post!

            I was thinking about the difference % values for dairy vs eggs. I have a question. (You may have already answered this and I just didn’t understand what you wrote.)

            Is it possible that the egg % would change if they evaluated eating just the egg white instead of the whole egg? I ask because lots of people ask about eating egg whites only. I was wondering if eating the whites only might involve an even higher IGF-1 risk compared to eating the whole egg. I suppose it might depend on whether we were talking about replacing the yolk with the same number of calories of egg white? I don’t know if this question makes any sense or not…

            1. Bear in mind, the study we’re discussing is rather noisy. Aggregate effects on IGF and its BPs were estimated by multivariate regression on macronutrient sources from dietary questionares and blood samples in 4700+ subjects, but the effect sizes were small and the only protein source where a statistically significant effect was seen was with dairy protein and dietary calcium (ie associated with dairy in general population cohorts).

              Ignoring the ethical concerns with the egg industry for a moment, egg whites are a rather complete protein source unsullied by the high-leucine and micro-RNAs of dairy. Its these factors that may responsible for the uniquely potent effect of dairy protein on IGF-1. However, of all food proteins, egg whites have the highest methionine content, and excess methionine in particular has several unique concerns.

              Dr. Greger has addressed the methionine dependancy of many cancers. This appears due to common DNA deletion in cancers that spans both the gene for tumor suppressor p16 and an adjacent gene for a methionine salvage enzyme (methylthioadenosine phosphorylase). But even in a hypothetical persons free from occult/hidden cancers, excess methionine increases homocysteine, associated with many disorders. While it was once believed homocysteine was an independent cause for cardiovascular disease, scientists have induced atheroclerosis with high methionine diets independent of homocysteine levels, and high methionine diets increase coronary risk in humans.

              Methionine restriction experiments have been a particular focus in experimental gerontology for the past decade, because they provide a practical (with vegan diet) approach for healthspan extension. Part of the benefit owes to delay of cancer in tumor prone animals, but interestingly, they’ve also demonstrated that excess methionine is unique among amino acids in increasing free-radical generation by mitochondria. In other words, methionine is an important pro-oxidant, undoing our other efforts with anti-oxidant foods.

              If you’re curious, here are some 70+ papers on health effects of methionine. My readings have lead me to adopt what may be an original to me “high (G+S)/(M+C) ratio” diet, which I briefly discuss here (ie, low-fat whole foods plant based with a focus on legumes, nuts, and buckwheat & oats among grains).

              1. Darryl: Thanks so much for this reply! I found it really helpful and interesting. I’m going to save this information and use it when people ask about eating egg whites, assuming you don’t beat me to it. :-)

                Thanks again!

  6. I love your videos. They take complicated biochemistry and make it easier to understand. When I did a google search, I was actually looking for the benefits of IGF-1 and its relationship to DHEA. I appreciate your videos and the only people who I know who cured their cancer did it by eating vegan and juicing (vegetables and in some cases, marijuana). It seems that animal protein that promotes IGF-1 would be good for children, since they need to grow but not so good for adults who have cancer. This is similar to folic acid. Folate from plants is not known to promote cancer growth but synthetic folic acid is known to encourage the growth of existing tumors. It should not be added to our grains for that reason. But it prevents neural tube defects in fetuses and folate prevents damage to DNA. I still think that I do well on my 80% raw vegetarian diet that includes some eggs from my own hens (who are pets).

  7. I’ve been searching for information for my post-graduate students regarding cellular metabolism and cancer. Thank you for some practical applications and explanations. I am also vegan by choice for health and have had the energy to run my first marathon at the age of 61! Also, joint pain is GONE!

  8. My bride of 57 years is trying to avoid a breast cancer recurrence and is going vegan. We can’t find out if goat cheese (or any NON cow cheese) is free of IGF-1, which we are trying very hard to avoid. Does anyone know if it is safe and free of the IGF-1? an email to me would be appreciated.

    1. I’m a little confused by your question @searcher since vegan = no animal product foods. Goat cheese is not vegan or plant based. I’m not sure about the IGF-1 level of goat cheese, but it is probably best to avoid it. My recommendation is try experimenting with making a cashew “cheese” as an alternative. Also, be sure that you and your bride check out the cancer videos on this site, they are priceless.

    2. My understanding is that the amino acid leucine, which is in all dairy products, triggers IGF-1 and insulin signalling. If you must eat cheese every once in a while, cheese from sheep that feed on pastures is higher in CLA than cow and goat cheese. I know that cashew cheese is delicious, but as a cancer survivor, I’m avoiding cashews because they’re high in copper.

  9. Hello, here is a question I’d like answered. If you fast fro four days why does that lower your IGF 1. If you fast for two days a week will this also lower your IGF 1. I just don’t want to become a vegan. Thank you

    1. The whole point of this video series is to say that we should REDUCE IGF-1 for the exact opposite reasons. Increasing IGF-1 means promoting the growth of tumors.

  10. What do you think of the protein powders produced form the milk? And what about the egg? Is it classified as animalic or veg. Prot.?… Thx

    1. Eggs should be avoided for multiple reasons.

      Consuming protein powders does nothing more then cause weight gain, as excess protein will be stored as fat. All the protein you need comes from diet alone, and as long as you are eating when your hungry, till your full, you will never become protein deficient.

  11. you might be interested in my diet. For about five years now I’ve been living almost entirely on skim cow’s milk. Every day I drink about two gallons (7.5 liters) of skim cow’s milk, and hardly eat or drink anything else. It has been great for my health.

  12. Luigi Fontana’s study indicated that a reduced intake of protein ( 0.8 grams per day per kg of body weight) would lower IGF-1. However, I’m now seeing that animal protein tends to be the culprit rather than plant-based proteins. My question is, then, if I should just track my animal protein intake and, if so, what would be the “reduced” RDA (per kg body weight)?

  13. On the recent “Study” comparing Protein consumption to Smoking, I thought I’d comment.

    The authors of the dreadful Protein/Cancer/Cigarettes report failed to include their supplemental data therein, but I did find it and carried out a brief analysis; unless I’m missing something, this Study is far worse than the average epidemiological one. That is because it seems that it’s not just poor in that the claims were made without proper causation (the usual problem with epidemiological forays) – in fact it appears they should have known from the data that their conclusions were effectively impossible to claim. See my brief analysis below, and decide for yourself:

    Insulin and IGF-1 can be driven up by sugary rubbish too….

  14. Dr Greger

    Does this include Milk, Egg, and Whey protein powders ?
    Do these powders in isolated protein supplement form have the same resulting igf1 influence?


  15. As one of the Moderators for, I see you asked if protein powders from isolated protein milk, egg and whey can cause the same harmful igf-1 influence. I’d suggest you look at the ingredients for those powders. If they were created using the animal proteins of egg, milk and whey, then we can expect them to have the same negative effect. I did a search looking a studies investigating IGF-1 and the intake of animal v plant protein and there is clear indications that a plant-based diet is associated with lower circulating levels of total IGF-1, discerning if the animal protein came directly from the animal or was in supplemental form was not attempted. See one excellent study with methodology making this point; The Associations of Diet with Serum Insulin-like Growth Factor I and Its Main Binding Proteins in 292 Women Meat-Eaters, Vegetarians, and Vegans. Because an animal protein is processed and made into a powder wouldn’t make it less likely to be negatively affected by IGF-1. Again, best to stick to whole foods and recognize the effects of animal protein.Other videos detail the effects of animal proteins on the body. You may want to check out : for further discussion of the IGF-1 protein relationship.
    I hope that helps.

    1. So we know for sure the animal proteins are what influences igf1 levels?

      Is it, e.g., the hormones and whole proteins themselves in the animal products and animal fats?

      Do we know if it’s the individual amino acids or whole proteins, antibodies, and hormones ?

      Do we know which amino acids and which whole proteins to avoid?

      ***Clearly ingesting individual amino acids must have a different effect than ingesting animal hormones, fats, antibodies, etc….????? ***

      Also, do grass fed varieties of butters and meats provide a more favorable food ? I understand they improve Omega 3 to Omega 6 ratios but what else is there to know…. What else has been studied? I have heard CLA is higher bur have heard mixed things about CLA….

      I was an avid bodybuilder where I was trained to eat high Biological Value protein like whey and egg for their Branched Chain Amino Acids. But now, I am older with 2 young boys 3 and 8.
      I want to make sure they are getting the right foods. I would go completely vegan if I knew for sure it was 100% the best for us. I just have my doubts because I see the b12 deficit thing in vegans that points to a possible ancestry of omnivores with animal products sprinkled in.

      I want to do what’s best for my family but I am worried going vegan could be estrogenic (soy, phytoestrogens, etc….) for my young boys and leave them with possible deficits in growth to adulthood.

      Also, what is your take on glyphosate? Is it as prolific and dangerous to gut flora as mentioned in the news and tv?
      Does Organic really lower glyphosate levels? Glyphosate in meat eaters vs vegans and gut health of same?

      Leaky gut and autoimmune disorders in vegans vs meateaters??

  16. May I ask a question that has been bugging me and can’t get the answer to.
    Fasting and resistance exercise increases HGH+IGF1 and HGH by 2000% if they are done together, @20-23hrs lets say, will this ‘internally’ generated growth hormone surges also pose a potential problem if one has pre-cancerous condition such as polyps,tumors etc., as would eating meat/dairy etc?

    I have gallbladder polyps and trying to shrink them by doing intermittant fasting and eating once a day to get my body into autophagy (self eating) in a bid to shrink the polyps,I have to go to have scans every 6 months, if they get to a certain size (Grow) then they can turn malignant and so I started worrying that what I was doing with the fasting could actually make the polyps grow, i.e. increase growth hormone. Please someone help me out with this question.

    I suppose I could try other avenues to increase autophagy via exercise and protein restriction. Thankyou.

    1. Hey Gerald, thanks for writing! I think the latter strategy you proposed here is much more realistic; anyone can do a plant-based diet and exercise, but fasting and eating once per day is highly experimental and unproven in its effects. Polyps are abnormal growths and they should regress without constant stimulation by growth factors that are increased by animal protein.

  17. Question for Dr Greger-
    I am working with a patient, the above studies that you mention (protein intake and IGF-1 levels and the one that looked at non animal protein vs animal protein intake and IGF-1 levels? I am interested in reading them.

    1. Hi Carolyn,

      Here are all the studies featured in this article:

      You should be able to access the entire article for the first and last studies I linked to, but will unfortunately need some kind of institutional access to access the second article. I hope this helps!

      Thank you.

  18. I’ve got what seems to me to be a crucial question. Two, really. 1) I wonder if high IGF levels are bad only in non-athletes, or if they are bad also in athletes. Because athletes trying to maintain high muscle mass : bodyfat ratios seem to benefit in this goal from high IGF levels. Further, high HgH levels seem related to youthfulness, by inductive reasoning perhaps, but there is a coincidental relationship between aging, and drastically-reduced HgH levels. Further, this link extends to sleep quality: aging is definitely linked to poor sleep quality, which is linked to weaker/shorter periods of Delta sleep, which is linked to lower levels of HgH, which is linked to higher bodyfat and reduced muscle mass retention. And since muscle retention seems to be linked to IGF levels, and since IGF is a metabolite of HgH in the liver, it is difficult to conclude that high IGF levels are bad. They seem to be linked to youthfulness/good sleep/high HgH levels/lower body fat/higher muscle retention. So much so, that I’ve been taking aminos that stimulate HgH production in the pituitary, and I’ve been taking herbs that are known to improve Delta power and duration such as Ashwagandha.

    But it occurs to me that high HgH levels might be good only in athletes, e.g., in people who USE the extra hormone. IGF levels resulting from HgH metabolism in the liver might be good only in people who USE the substance in the muscle to build muscle mass. Therefore, without the external demand for muscle building that results from athletic activity, you just have a bunch of otherwise useless HgH floating around, with nothing useful to do except stimulate the growth of cancer cells. An important principle in bio-hacking: “Use it or lose it.” Excess testosterone, for example, instead of being used to build muscles that aren’t being stimulated, aromatizes into estrogen, which has the homeostatic effect of reducing the output of T from the testes.

    I doubt it will surprise you to learn that I myself lift free weights heavily about 4 times/week, and high-intensity interval train at least once/week. I want to re-apprehend the high ratio of muscle to bodyfat that I had when I was younger, so anything that INCREASES my IGF seems to me like a good thing. BTW, good sleep and the right herbs and good antioxidants are known to reduce the incipience of cancer cells, so I’m frankly doubtful that IGF *causes* (or incipiates) cancer cells… my suspicion is that IGF, because it is a GROWTH factor, causes *already incipient* cancer cells to grow and metastasize, NOT for new ones to form from cells with corrupted DNA. So if I’m already diligent to prevent initial incipiation of cancer cells, IGF will only help HEALTHY cells grow faster, given the stimulation I’m providing with my lifting.

  19. Hi, thanks for asking!
    In November of 2017, at 63 years old, my sister was diagnosed with StageIV pancreatic cancer that had metastasized to her liver. Unable to have the WIPPLE surgery, she joined a clinical trial at UTSW in Dallas. Their dietician even promotes animal protein.

    Neither she nor her husband will accept the proof about animal protein. So, here we are in July, 2020 and she is still in the trial and her CT scans are always good.

    Since writing this comment, I have made up my mind to send a letter to her pancreatic oncologist and ask him why he doesn’t put her on a vegan diet. He knows me because I attended every one of her chemo treatments for the first year.

    Discouraged, I ask myself how dare I contact one of the best pancreatic oncologists in the country. UTSW is the research division of the University of Texas.

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